A draft bill to legalise gay marriage in France unveiled on Wednesday is a "sham
that will smash one of the foundations of society," the head of the
Catholic Church in France has warned.

Paris Archbishop Andre Vingt-Trois said the bill on "marriage for all" allowing same-sex couples to wed undermined a child's basic right "to know one's parents and be raised by them".

It was the latest warning against the Socialist-proposed law from church leaders, some of whom are calling for the French to take to the streets to vent their opposition, and some sections of the mainstream Right.

President Francois Hollande pledged in his manifesto to legalise gay marriage. While a majority of French people approve the change, support has dropped to 58 per cent according to the latest poll – down five points since last year – while the French are split over same sex adoption.

With the draft bill presented to the cabinet today ahead of a parliamentary debate in January, Cardinal Vingt-Trois told a meeting of bishops in Lourdes: "It would not be 'marriage for all'. This would be the marriage of some imposed on all.

"It is important to remember a number of fundamental rights, which are the result of the accumulated wisdom of our civilisation that marked its gradual exit from barbarism.

These included the fact that "every child born to this world has the right to know who engendered it and to be raised by them".

He also lambasted government plans to ban the words "mother" and "father" from all wedding ceremonies and official documents.

But Cardinal Vingt-Trois added: "Has anyone asked citizens if they agreed to no longer be the father or mother of their child and become parent A or parent B?"

"A vision of humans that fails to recognise sexual difference would be a sham that would smash one of the foundations of our society," he warned.

Last month, French Cardinal Philippe Barbarin also predicted that marriage would "herald a complete breakdown in society", including rising "polygamy, paedophilia and incest." Pope Benedict recently urged French bishops to speak out against the new law, saying it followed "a concept of human nature that has proven defective".

Jean-Marie Le Guen, Socialist MP for Paris said the Church's vitriolic opposition marked a "shocking step backwards" and a "return to fundamentalism".

French bishops should "open their eyes to families who today make up society – single parent, single sex or recomposed families," said Erwann Binet, the Socialist who drew up the law.

Gay rights group SOS homophobie pointed out that other European countries that have introduced gay marriage and adoption, including Spain and Portugal, had "not descended into the decadence they herald. None now question this just reform."

Right-wing former Prime Minister François Fillon promised to reverse the law should his camp win back power, while 100 mayors in France signed a petition saying they reserved the right to refuse to preside over same sex marriages.